Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$116.91	5.432%	$123.2606	$123.26	$123.25	$123.30
Purchase #2	$236.45	10.299%	$260.802	$260.80	$260.80	$260.80
Purchase #3	$184.80	11.705%	$206.4308	$206.43	$206.45	$206.40
Purchase #4	$76.38	13.192%	$86.456	$86.46	$86.45	$86.50
Purchase #5	$201.38	13.431%	$228.4273	$228.43	$228.45	$228.40
Purchase #6	$196.42	9.373%	$214.8304	$214.83	$214.85	$214.80
Purchase #7	$91.78	12.561%	$103.3085	$103.31	$103.30	$103.30
7 purchase totals =	$1,104.12		$1,223.5156	$1,223.52	$1,223.55	$1,223.50